The output powers from the two ends of a DFB region were compared. The power ratios and the external differential quantum efficiencies of the lowest-threshold modes were calculated in detail for an asymmetric end structure, one end being a cleaved facet and the other end being non-reflective. Power ratios of 2–5, depending on the corrugation phase at the cleaved facet, were predicted for KL=2–3. Such large ratios were actually estimated experimentally in InGaAsP/InP DFB lasers with a window region at one end. A larger output from a window region may be useful if the window region length is restricted, to about 10 µm or less in this case. The asymmetric output power in an FP-type DFB laser was also demonstrated.
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